N[4-(Trifluoromethyl)phenylliodacetamide, "TPI", has been synthesized, and it is sought to know its elemental composition. This composition, together with its 1-H and 19-F spectra, will be used to confirm the structure of TPI. Authentic TPI will be reacted with Cys-707 of myosin, thus endowing myosin with an NMR (19-F) "reporter" group. Hopefully this group will report conformational transitions thought to occur in myosin in the Oo-10oC range of temperature. More accurate positioning (better specificity) will be acheived by a corresponding (14-C) iodoacetamide synthesis.